Voltammetric and Electrochemical Impedance Study of Sm3+ Effect onto the Nickel Electrodeposition Process

In this work, cyclic voltammetry and electrochemical impedance techniques were used to study the effect of Sm⁺³ dissolved in the electrolytic bath, on nickel reduction process. The results obtained by cyclic voltammetry showed that, during nickel electroplating without Sm⁺³, three reduction processes were observed and they may be related to the adsorption and/or reduction of H₂, H₃BO₃ and Ni⁺². On the other hand in presence of samarium, the Ni electroplating process is clearly affected; an additional reduction process and overpotential for Ni reduction can be observed. With the purpose of elucidating the processes attributed to the electroactive species of Sm⁺³,cyclic voltammetry studies were carried out employing a solution of sulfamic acid + samarium. These results shows the presence of a reduction process in a potential window of -0.77 to -0.82 V vs. SCE and the corresponding oxidation process (-0.54 to -0.57 V vs. SCE), indicating the presence of the redox couple Sm⁺³/Sm⁺². Finally, the results obtained by electrochemical impedance technique indicate that during the electrodeposition of Ni, in the presence of samarium, resistance to charge transfer increases considerably. This increase can be attributed to the formation of a film of oxide or hydroxide of samarium.